This tag is for questions about the foundations of mathematics, and the formalization of mathematical concepts in foundational theories (e.g. set theory, category theory, and type theory).

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How do you multiply infinite quantities?

Out of curiosity I was watching this video from njwildberger on youtube: https://www.youtube.com/watch?v=4DNlEq0ZrTo Where he says that you can't define associativity between irrational numbers ...
5
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1answer
102 views

How much maths can we do in NF(U)?

I have recently become interested in non-standard set theories, particularly in NF and NFU and have been reading some things here and there. Of course, I don't know much about it and I'm still trying ...
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42 views

Propositions as sets of witnesses

Under the propositions-as-types paradigms, a proposition is identified with the type of all its proofs. From a more classical perspective (and assuming the full-blown axiom of choice), it sometimes ...
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4answers
196 views

A question regarding ❋166.44 in Whitehead & Russell's Principia Mathematica

In the first step of Dem, I wonder how $\Sigma ‘\times P^{;}Q$ is transformed into $\Sigma‘ \Sigma^;(P \overset{\downarrow}{.,})\dagger^; Q$. Thanks,
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1answer
128 views

Is there a reasonably strong foundation for mathematics that can prove its on consistency?

Ever since I have read about both Gödel's incompleteness theorem(s?), which I believe roughly means: "A system at least as strong as Peano arithmetic cannot prove its own consistency." and learned ...
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74 views

Well Formed Expression (Polish Notation)

In Kunen's book Foundation of Mathematics the definition of a well formed expression (wfe) of a lexicon for Polish notation $\langle W, \alpha \rangle$ ($W$ is a set and $\alpha:W\to\omega$ is a ...
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45 views

Codifying ways to think and write about imprecise ideas?

This question will not be about affine spaces; rather those are mentioned here as one of many examples. A vector space has an underlying set and a field of scalars and an operation of linear ...
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2answers
40 views

Well-ordering principle and negative integers

The Wikipedia article on the Well Ordering Principle defines it [1] as: "The well-ordering principle states that every non-empty set of positive integers contains a least element." And it defines ...
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1answer
130 views

Proof correctness problem

I was watching this talk by Vladimir Voevodsky which was given at the Institute of Advanced Study in 2006. In his talk the first slide he shows has the following written on it: ...
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35 views

What do “completely described” and “complete formalisation” mean?

From Wikipedia In mathematics, an axiomatic system is any set of axioms from which some or all axioms can be used in conjunction to logically derive theorems. A mathematical theory consists of ...
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355 views

Escaping Gödel's proof

Is there any way in which a reasonably strong foundation of mathematics can get around the hypotheses of the incompleteness theorems?
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199 views

Does counting make sense?

The Bertrand Russells and Alfred Whiteheads of this world have written lengthy proofs that $1+1=2$, etc. (and one should hope their purpose was to illuminate some point about mathematical logic rather ...
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1answer
28 views

Is there a way to quantify distance between formal systems?

Suppose I and my twin embark on a project. I create a mathematical system, from scratch, based on the ZFC axioms. My twin, having read the HoTT book, decides to ground his system there. Does there ...
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2answers
153 views

What is the meaning/purpose of finding the “foundations of mathematics”?

I've read in a lot of places how there was a "foundational crisis" in defining the "foundations of mathematics" in the 20th century. Now, I understand that mathematics was very different then, I ...
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2answers
91 views

exercise in Tao analysis I book

I am supposed to prove that if a is a positive natural number then there exists exactly one number b, such that the increment of b is equal to a. My idea was to induct from the base case a = 1, but I ...
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0answers
110 views

If physical space had cardinality larger than $\aleph_1$, would we need new math to describe dynamics? [closed]

If physical space had cardinality larger than $\aleph_1$, would we need new math to describe dynamics? For instance, would the dynamics of a sea of virtual particles of cardinality $\aleph_1$ would ...
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4answers
344 views

What is your intuitive understanding of infinity? [duplicate]

What is your intuitive understanding of infinity? Mine is the following, I prepared it as image: Those were the main points I got to after thinking by myself about what infinity is, without ...
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1answer
116 views

Does every mathematical principle have a proof?

My question actually narrows down to the meaning of mathematical principle. While I'm looking for some principles, they usually have their proofs, so I thought "principle" has the same meaning as ...
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4answers
380 views

The standard role of intuitive numbers in the foundations of mathematics

In my career I've been formed mostly in the formal side of mathematics, that is, standard set theory and every classical branch of mathematics that uses set theory. However, I am not quite sure about ...
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4answers
72 views

A Basic Truth of Set Theory?

Forgive me in advance if this question seems ridiculous. Let $X$ be a set. Then "$X\neq\bigcup_{x\in X}\{x\}$ is false" is a true statement. This statement says that a set is always equal to the ...
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1answer
77 views

On the number of countable models of complete theories of models of ZFC [duplicate]

Fix the language of set theory $\mathcal{L}=\{\in\}$. Let $\langle M,\in\rangle$ be a set or proper class model of ZFC (e.g. $M$ could be $L$, $HOD$, $V_{\kappa}$ for some inaccessible cardinal ...
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1answer
65 views

How do definitions work in Martin-Lof type theory?

The classical viewpoint is that we can found mathematics by specifying a formal system $F$ whose theorems are precisely those of ZFC. However, since $F$ has essentially no support for the concept of a ...
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2answers
103 views

The rule of operator “+”

1.It is natural for us now to see the natural number $1,2,\cdots$ and the operator "+", but for me it is hard to see how we define "+", i.e. I can't see the rule of $a+b$. 2.Another question is how ...
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1answer
341 views

Term for: There Exists a Rational between every two Rationals?

The integers and the rationals have the same cardinality, but the rationals satisfy the property that: $$ \forall p,q\in\mathbb{Q},\quad \exists r\in\mathbb{Q}\quad \textrm{s.t.}\quad p<r<q, $$ ...
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1answer
74 views

Is there way to formalize the idea that a category can be “cocomplete from the inside”?

Let $\mathrm{KSet}$ denote the category of all countable sets, including the finite ones. Then $\mathrm{KSet}$ is finitely complete. Furthermore, $\mathrm{KSet}$ admits all countable colimits, or, ...
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190 views

How is geometry defined using ZFC?

I've been trying to get a rigorous understanding for the mathematical concepts I learned in high school. I've been reading about how the real numbers can be constructed from the axioms of ZFC, but I ...
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2answers
92 views

Are axioms chosen with the goal of “making things work” instead of some deep philosophies?

Are axioms chosen with the goal of "making things work" instead of some deep philosophies? If everything should be deducible, that is, provable from something else, then in this chain of deduction ...
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2answers
100 views

Is there a (foundational) type theory with the features I'm looking for?

I like to distinguish between sets and subsets. We imagine that sets are floating free in the universe, and that the elements of a set are constructed according to some kind of recursive rules. Like ...
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1answer
66 views

Study of all published works of Bertrand Russell on foundations of mathematics: Please recommend his works.

Study of all published works of Bertrand Russell on foundations of mathematics: Please recommend his works. I think Bertrand Russell was a special mind and I set a goal for myself to study all his ...
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1answer
80 views

How functions definided by cases, can be written in formal ZFC set theory?

Function definition by cases. It is usual define for example the absolute value of Real number as $$ \left|x\right| = \begin{cases} x & if & x> 0 \\ -x & if &x < 0 \\ 0 & ...
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1answer
70 views

What is the real meaning of Hilbert's axiom of completeness

According to Greenberg's book of geometry it is sufficient to consider the axiom of Dedekind along with Hilbert's axioms (except of course for the Archimedian Principle and his Axiom of Completeness) ...
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3answers
123 views

Disturbing the foundations of mathematics

I was curious of knowing if it is possible that an event "x" could disturb so greatly mathematics that we could be casting doubts on all the achieved results from the very beginning. I'm not sure if ...
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1answer
158 views

Why should we accept the existence of subsets $A$ such that neither $A$ nor $A^c$ are recursively ennumerable? And how can we persuade others?

Encode every pair $(t,x)$ (where $t$ is a Turing machine and $x$ is an input string) as a distinct natural number. Then the halting subset $H$ fails to be recursive. $$H := \{(t,x) \in \mathbb{N} ...
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1answer
71 views

When is it useful to reduce mathematical objects to foundational levels and when it is not?

When is it useful to reduce mathematical objects to foundational levels and when it is not? Let's say you work in the field of computer vision, or else. How can you claim your method is optimal if ...
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3answers
147 views

Are there other approaches for the foundations of mathematics, other than logic and set theory?

Are there other approaches for the foundations of mathematics, other than logic and set theory? And why does set theory begin talking about objects and groups of objects. Is it proven somewhere that ...
2
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1answer
62 views

Question about the univalence axiom versus skeleta.

Here, Dan Licata writes: [Univalence] can be used to build algebraic structures in such a way that isomorphic structures are equal (e.g. equality of groups is group isomorphism). He writes ...
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294 views

Is formal logic necessary for pure/“higher” mathematics?

I'm asking this as an autodidact who wants to learn math rigorously for its own sake. And I was just wondering if understanding proofs could be achieved without a formal grounding in symbolic logic. I ...
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2answers
58 views

Integers, rationals and reals as sets? [duplicate]

Natural numbers can be represented as pure sets by defining them to contain every number that is smaller than them. Arithmetic can be performed on them using the Peano axioms. Are there any similar ...
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2answers
89 views

Consistency of ZFC and the key assumption [closed]

I recently read this answer to a MathOverflow question that got me thinking. Very roughly, here's what the author of that answer says: Gödel's second incompleteness theorem implies that if there ...
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3answers
96 views

Mathematical logic and foundations of mathematics in the 20th century

I would like some references regarding the foundations of mathematics in the 20th century, and mathematical logic, e.g. (1) I want to understand what happened to the foundation, what originated the ...
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0answers
121 views

Are there any good documentary films about the continuum hypothesis?

Are there any good documentary films about the continuum hypothesis? I'm looking for something slightly more serious than the usual "Cantor showed that infinity plus one equals infinity and then went ...
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10answers
9k views

Why can't you add apples and oranges, but you can multiply and divide them?

What is the algebraic difference between arithmetic operations, that prevents entities with different units from being summed or subtracted, but allows them to be multiplied or divided? This looks ...
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1answer
145 views

Can all math results be formalized and checked by a computer?

Can all math results, that have been correctly proven so far, be formalized and checked by a computer? If so, what type of logic would need to be used there? I've heard that the first-order logic is ...
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89 views

Dividing line between useful ( for non-foudational Math ) and unnecesary, in Foudational Math.

I started studying mathematical logic because I was curious about the behind-the-scenes of proofs, theorems and axiom systems of math. I'm interested in understanding the big picture that ...
2
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2answers
86 views

Goedel's completeness theorem in and/or for intuitionistic first order logic

Warning: I am neither a logician nor a set theorist, just curious about foundations of classical and intuitionistic mathematics. Therefore it might well be that the things to come are plain wrong, and ...
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1answer
202 views

New Axioms of Infinity

Axiom of Infinity says there is an inductive set (i.e. a set which includes $\emptyset$ and is closed under successor operator). Formally: $Inf:\exists x~(\emptyset\in x~\wedge~\forall y\in ...
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60 views

Defining the number $ e $

In this YouTube video it is said that $ e $ naturally arises as a number that allows us to take the derivatives of functions like $ a^x $. So $ e $ is defined as a number for which: ...
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49 views

Variable theory

I wanted to know if there's any alternative variable theory to Russell's used in his Principia. I mean, the modern definition of "variable" and "constant" still follows his works? I try to search on ...
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142 views

Do the Kolmogorov's axioms permit speaking of frequencies of occurence in any meaningful sense?

It is frequently stated (in textbooks, on Wikipedia) that the "Law of large numbers" in mathematical probability theory is a statement about relative frequencies of occurrence of an event in a finite ...
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112 views

Where can I find information about metametalogic

I have been looking for information about metametalogic (theory about metalogic) but I found basically nothing. I would be grateful if anybody could refer me to a book or a publication. thanks.